Heretofore, a conventional power plant which comprises a capacitor connected with a positive electrode bus and a negative electrode bus of an inverter circuit for supplying three-phase alternating current power to an electric motor and a direct-current power source connected with the positive electrode bus or the negative electrode bus of the inverter circuit and a neutral point of the electric motor has been proposed (for example, Japanese Patent Laid-Open Publication No. Hei 10-337047, Japanese patent Laid-Open Publication No. Hei 11-178114, and the like). In this device, a circuit comprising a coil of each phase of the electric motor and a switching element of each phase of the inverter circuit is caused to function as a booster chopper circuit for accumulating electric charge in the capacitor by increasing a voltage of the direct-current power source, and the electric motor is driven assuming that the capacitor in which electric charge is accumulated can be considered to be a direct-current power source. Switching operation of the switching elements of the inverter circuit which is executed at the time of applying the three-phase alternating current to the electric motor causes simultaneous control of driving of the electric motor and control of the accumulation of electric charges in the capacitor.
However, in such a power plant, there are situations where the electric motor cannot be driven with a desired output because, although the power plant can operate at full performance when the direct-current power source has a normal temperature, when the temperature of the direct-current power source is low, such as at a start-up time of the electric motor, the rate of chemical reaction inside the direct-current power source slow down then internal resistance of the direct-current power source increases. Under such conditions, therefore, the performance of a battery is sometimes less than optimal.
Further, because an output of the direct-current power source decreases even when the direct-current power source has a high temperature, it is preferable to maintain the temperature of the direct-current power source within an appropriate range in order for the power plant to perform at its maximum potential. Still further, in order to carry out stable boosting operation of a power conversion section which functions as the booster chopper circuit in the power plant described above, it is preferable to maintain the temperature of that section within an appropriate range.
Such circumstances are similarly applicable to the temperature of a direct-current power source and a temperature of a DC—DC converter in a device in which boosting operation of a circuit comprising a coil of each phase of an electric motor and switching elements of an inverter circuit is executed by the DC—DC converter as a substitute, namely a power plant in which DC—DC conversion of a direct-current voltage coming from the direct-current power source flows into the DC—DC converter, direct-current power is accumulated in a capacitor, the direct current power accumulated in the capacitor is converted into three-phase alternating-current power by switching operation of the switching elements of the inverter circuit, and the three-phase alternating-current power is supplied to the electric motor. The situation is comparable for temperatures in a drive unit in which DC—DC conversion of a direct-current voltage from the direct-current power source is performed by a DC—DC converter, direct current power is accumulated in a capacitor, and the directcurrent power accumulated in the capacitor is supplied to an electrical appliance (a load).
An object of the power plant and the control method according to the present invention is to solve such problems and to maximize performance of the power plant by maintaining appropriate temperatures for the power source or the power conversion section. Further, the power plant according to the present invention is directed to rapidly heating up the power source which has a low temperature so to enable maximum performance of the power plant. Further, the power plant according to the present invention is directed to restraining the power conversion section from increasing the temperature so as to maximize the performance of the power plant. Further, the present invention is directed to providing a vehicle capable of maintaining a more appropriate temperature in the power plant so as to improve performance of the power plant. The storage medium and the program according to the present invention are directed to causing a computer to function as a control device for maintaining more appropriate temperature conditions for the power source or the power conversion section.
Further, the drive unit according to the present invention is directed to maximizing performance by maintaining more appropriate temperature conditions for the power source or the DC—DC converter. Further, the drive unit according to the present invention is directed to maximizing performance by rapidly heating up the power source when the temperature of the power source is low. Further, the drive unit according to the present invention is directed to maximizing performance by restraining the temperature of the DC—DC converter. Further, the present invention is directed to providing a vehicle which maintains a more appropriate temperature in the drive unit so as to maximize the performance of the drive unit. The storage medium and the program according to the present invention are directed to causing a computer to function as a control device for maintaining more appropriate temperatures for the power source or the DC—DC converter.